The standard procedure of making a steel part with regions of different ductility comprises the steps of sequentially:                passing the part on a rack through a furnace and heating it therein to above the AC3 point of the alloy;        shaping and hardening the part in a press, which process hardens the entire part;        removing the part from the press; and        targeted reheating of predetermined regions of the parts to increase ductility in these regions.        
In automobile manufacture more and more structural parts of sturdy and high-strength steel are being used to meet the lightweight construction criteria for rising demands on material tolerances. This applies also for vehicle body construction, where for example structural and/or safety parts such as door impact pillars, A and B columns, fenders or longitudinal and cross beams are being manufactured from heat-shaped and press-hardened strong or high-strength steel more and more frequently to meet weight goals and safety requirements.
DE 24 52 486 discloses a method of shaping and hardening sheet steel with minimal material thickness and good dimensional stability, in which a sheet of boron-alloy steel is heated to a temperature above the AC3 point and is then shaped in less than 5 seconds into the final shape between two indirectly cooled tools with substantial shaping. Then it is subjected to rapid cooling while still in the die to produce a martensitic and/or bainitic structure (direct thermoshaping). These measures produce a product having good dimensional accuracy and high mechanical strength, a product that is eminently suited for use as a structural and safety part in an automobile.
It is also known from the prior art to first cold-preform a sheet metal blank made of boron-alloyed steel in the unhardened state, then to heat the pre-shaped part to a temperature over AC3 and then to shape it in under 5 seconds into the final shape between two indirectly cooled tools and subject it to rapid cooling while still in the die to produce a martensitic and/or bainitic structure (indirect thermoshaping). In this process the degree of pre-heating can reach 100% of the finished shape so that the part is first and foremost calibrated to size in the finished shape in the thermoshaping tool. Both the direct and the indirect process are referred to below as thermoshaping and press-hardening.
U.S. Pat. No. 5,972,134 discloses providing a sheet metal blank of hardenable steel for making a shaped metallic part for an automobile part having regions with high ductility, then first homogeneously heating this sheet metal blank to a temperature between 900° C. and 950° C., and subsequently shaping the sheet metal blank in a shaping tool into the shaped part. Finally the shaped part is tempered while still in the shaping tool to then bring adjoining partial regions of the shaped parts to a temperature between 600° C. and 900° C. in a time of less than 30 seconds. In this way, regions with high ductility are shaped in the sheet metal blank. At temperatures between 600° C. and 900° C. substantial structural transformation takes place in the grain of the steel, meaning that the mechanical values are redirected in the direction of unhardened steel. The steel is accordingly no longer high strength in the ductile regions. This patent proposes undertaking partial thermal treatment on the shaped part fixed on a feed mechanism by means of inductive heating.
US 2007/0107814 describes a thermoshaped and press-hardened structural part that has been thermotreated following a heat-forming and press-hardening process at 320 to 400° C. The high-strength properties of the part are locally influenced by this thermal treatment. The yield strength Rp0.2 and the expansion A5 remain virtually unchanged. Only the tensile strength RM is reduced by 100 to 200 N/mm2. With a grade of steel composed in weight percent of                Carbon (C) 0.18% to 0.3%        Silicon (Si) 0.1% to 0.7%        Manganese (Mn) 1.0% to 2.5%        Phosphorous (P) maximal 0.025%        Chromium (Cr) to 0.8%        Molybdenum (Mo) to 0.5%        Sulfur (S) maximal 0.01%        Titanium (Ti) 0.02% to 0.05%        Boron (B) 0.002% to 0.005%        Aluminum (Al) 0.01% to 0.06%, and        balance iron, including contaminants conditional on steel production,a tensile strength Rm of 1200 to 1400 N/mm2, a yield strength Rp0.2 of 950 to 1250 N/mm2 and an expansion A5 of 6-12% result following thermal treatment at 320 to 400° C. The material still has the required high-strength mechanical properties, though due to the slightly lower tensile strength Rm the material is so ductile that it puckers under load instead of breaking or tearing.        
U.S. Pat. No. 5,916,389 discloses a method of manufacturing a sheet steel product by heating a sheet cut to size, thermoshaping the sheet steel between pair of tools, and hardening the shaped product by rapid cooling from the austenitic temperature while it is still between the tools, and finally processing the product such that unhardened regions remain in it and processing is carried out in such unhardened regions. In this process, there is an alternative whereby the entire product is hardened in the tools and then the regions in which the processing is completed are tempered in a separate process. In such a case the tempering can be done immediately after the procedure by a machine, such as for example a punch, which has a heating device such as for example an built-in induction element.
US 2004/0112485 and 2008/0041505 disclose a system where the interior of a furnace is partitioned into two longitudinally extending and transversely adjacent zones, and one of the zones is heated to a substantially higher treatment temperature than the other of the zones, which may or may not be heated. A steel workpiece is conveyed longitudinally through the furnace with a region of the workpiece moving exclusively through the one zone and another region of the workpiece moving exclusively through the other of the zones such that the regions are heated to different temperatures. The treatment temperature in one of the zone is above the AC1 point for the workpiece and the temperature in the other of the zones is close to or below the AC1 point for the workpiece. Thus the use of pass-through furnaces for heating parts to a temperature over the AC1 or AC3 point of the alloy is standard in current production of thermoshaped and press-hardened automobile parts.